.container .game {
  width: 800px;
  height: 600px;
  border: 2px solid;
  position: relative;
  margin: 0 auto;
  overflow: hidden;
}
.game .sky {
  background-image: url("../images/sky.png");
  position: absolute;
  top: 0;
  left: 0;
  width: 200%;
  height: calc(100% - 112px);
}

.game .land {
  background-image: url("../images/land.png");
  position: absolute;
  bottom: 0;
  left: 0;
  width: 200%;
  height: 112px;
}
.game .bird {
  background-image: url("../images/bird.png");
  position: absolute;
  top: 300px;
  left: 100px;
  width: 33px;
  height: 26px;
  z-index: 5;
}

.game .bird.swing1 {
  background-position: -8px -10px;
}

.game .bird.swing2 {
  background-position: -60px -10px;
}
.game .bird.swing3 {
  background-position: -113px -10px;
}

.game .pipe {
  position: absolute;
  width: 52px;
  z-index: 4;
}
.game .pipe.up {
  background-image: url("../images/pipe-down.png");
  background-position: bottom;
}
.game .pipe.down {
  background-image: url("../images/pipe-up.png");
}
.game .mask {
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  position: absolute;
  opacity: 0;
  transition: all 0.3s;
  background-color: rgba(0, 0, 0, 0.5);
  z-index: 8;
}

.mask .mask-tip {
  font-size: 30px;
  color: #fff;
}

.container .tip {
  text-align: center;
  font-size: 17px;
  color: #ccc;
}
